In scuba diving, for instance, a supply of air, or of an air-oxygen mixture, is typically fed to a mouthpiece of the scuba diver from a high-pressure tank. En route to the diver, the air passes via a first-stage pressure-reducing regulator to a second-stage regulator which, in turn, supplies the mixture to the mouthpiece, when pressure within the regulator is diminished upon the diver's inhalation.
Conventional second-stage regulators are usually provided with an inlet chamber connected to an outlet of the first-stage regulator, and an outlet chamber connected to a mouthpiece for the user. The outlet chamber is separated from the outside environment by an elastically deformable diaphragm that blocks an opening formed in the regulator body. The diaphragm is connected via a lever to a poppet which closes the passage between the two chambers. The pressure inside the inlet chamber is maintained relatively constant at approximately ten bars as the pressure in the tank varies, due to appropriate calibration of the first-stage regulator. When the user does not breathe, his or her lungs, the mouthpiece, the outlet chamber and the outside environment are at the same pressure. When the user inhales, however a vacuum is created inside the outlet chamber. This causes the diaphragm to bend toward the interior of the chamber, thereby moving the poppet, which normally closes the passage between the inlet and outlet chambers, to an open position.
Upon opening the passage between the inlet and outlet chambers, an overpressure is created in the outlet chamber, which causes the diaphragm to return to a resting position. This, in turn, moves the lever and returns the poppet to the starting position, at which the passage between the inlet and outlet chambers is closed once again.
In conventional second-stage regulators where the diaphragm and corresponding opening formed in the regulator body are circular in shape, the diaphragm is usually locked at an edge of the opening by a cover that is threadably engaged with, i.e., screws over, the opening. In the case of diaphragms and openings having a different shape, the diaphragm is typically positioned at the edge of the opening by attaching the cover to the regulator body by screws. While useful, the latter arrangement has been found unsatisfactory, in particular, during production, in requiring that metal bushings be provided inside the regulator body to serve as seats for the screws and, during assembly, by requiring tightening of the screws. Concurrently, there is also a need to increase the size of the diaphragm as much as possible to reduce the effort required by the scuba diver during inhalation, that is, to the extent that the overall dimensions of the regulator allow. To achieve this objective, however, diaphragms with a non-circular shape, particularly those having an oval shape, are desired that also have a suitable system for locking the diaphragm and closing the regulator.